Microfilm as a means of storing business documents offers many advantages including a more compact means of storing, more rapid access, having a long archival life, rapid speed of capture, and ability to make subsequent paper copies. However, when many of hundreds of thousands of documents are stored on microfilm per week, it is often desirable after a number of years to only preserve some of those documents by insuring that the microfilm may be selectively duplicated on a document by document basis. This duplication process may take place once every year or two and so over a long period of time, for example, fifty years, it may be necessary to make as many as twenty duplications of the microfilm. In the past, this has not been practical because by direct optical duplication, there is some loss of quality each time the copy is made.
The invention proposed herein overcomes this difficulty by using electronic techniques to generate the duplicate microfilm and along with the image itself is stored additional data, which may be used to control the scanning and the creation of subsequent generations of the microfilm in such a way that important parameters of the image are preserved.
Using this technique then, it would be possible to make high quality, multiple generations of microfilm and to monitor the quality throughout the useful life of the image. A further advantage is that quite often when copies of microfilm are made, it is customary to use negative film to produce copies from; this usually results in alternate generations of images to be positive or negative, with at least one generation being a wasted generation of film. Generally, the users desire the second generation copy to be the same sense as the original. There is a considerable disadvantage in going from positive to negative in alternate generations. This method and apparatus insures that it electronically maintains the sense of the copy as that of the original.
Another advantage of this method is that it helps make microfilm more compatible with the electronic office and computer environment. This insures that microfilm can be treated as other computer media, such as magnetic disc, magnetic tape, and optical discs as far as archival storage and ease of duplication.